1. Field of the Invention
This invention pertains to the calibration of an electronic output system for use with a color printer so that the final print obtained looks like an image obtained on a video monitor.
2. Background Art
It is a common objective of a printing system to obtain a satisfactory match between an output print and an image produced of the print on a monitor. Commercially available graphic systems (e.g., such as the Designmaster 8000 electronic prepress system, manufactured by Eikonix Corporation) employ calibration tools that allow an operator to compare and match color proofs with a color monitor display. The procedure begins by selecting a representative sample of pictures. The pictures are scanned into the machine and optimal color separations are generated for each of the pictures. Optimal color proofs are then made up from the color separations and compared to the scanned image on the color monitor. If a match is not immediately evident, the color monitor is adjusted by creating monitor/proof ink tables that are modifications of the calibrated ink tables provided with the equipment. Ultimately, the modified tables will produce a monitor display that most closely matches the variety of pictures that will be viewed over the course of production. In this way, the operator is assured that a printed copy will match editorial changes seen on the monitor display.
The same basic methodology has been used in photographic printing systems. For example, in U.S. Pat. No. 4,736,245, a photographic printing inspection system includes a preprocessing step in which a reference photographic negative (including a grey scale) is repeatedly printed until an optimal print is obtained. Then the original grey scale is scanned and displayed on a display monitor, and gradation tables in the display system are corrected until the video grey scale is identical to the grey scale included with the optimal print. With the monitor thus calibrated, the images on the monitor will accurately correspond to photographs subsequently produced by a color printer. As with the ink printing systems, the monitor is matched to an optimal hard copy, ending up with a monitor image that looks like the final output.
In many video or computer printing situations, however, the input is generated electronically. There is no optimal, real input image to compare to the monitor. Consequently, it becomes difficult to calibrate the monitor to look like a final print. Heretofore, as disclosed in U.S. Pat. Nos. 4,779,106 and 4,710,885, it has been the practice with such systems to form a printout of a stored video image, scan the printout into a processor, and then electronically compare the scanned data with the stored data to determine difference data which can be used to modify subsequent images. This is a technically complex procedure wherein the comparison is made electronically, rather than interactively by an operator, as in the ink and photographic systems.